A split is emerging in the Federal Reserve as officials worry that chairman Ben Bernanke's $85bn-a-month efforts to bring down unemployment may backfire.

According to the minutes of the last Fed meeting, released on Wednesday, a number of senior officials were concerned about the risks involved in the Fed's massive bond-buying programme, and warned that the initiative might be hard to stop in the future.

The news triggered a sell-off in the US stock markets, with all the major indices falling after the minutes' release. The Dow Jones Industrial Average closed down 108 points, erasing two days of gains.

Since the financial crisis, Bernanke has presided over a massive financial aid initiative with three rounds of quantitative easing (QE) aimed at stimulating lending and jobs growth. The latest round will reach $1.14tn before the first quarter of 2014, according to a Bloomberg survey of economists.

Bernanke is reportedly not seeking a third term as chairman, and the minutes show he clearly has the support of most Fed members. But they also provide the strongest sign yet that dissent towards his policies is growing.

"Several participants stressed the economic and social costs of high unemployment," the minutes said. "However, many participants also expressed some concerns about potential costs and risks arising from further asset purchases."

According to the minutes, "a number of participants" wanted closer scrutiny of the efficacy, costs and risks of the asset-purchase programme. They appear concerned that the risks of the program may now outweigh the benefits, and suggest the committee could reduce or stop the initiative before Bernanke hits his target rate for unemployment.

"A number of participants stated that an ongoing evaluation of the efficacy, costs, and risks of asset purchases might well lead the committee to taper or end its purchases before it judged that a substantial improvement in the outlook for the labor market had occurred," the minutes state.

However, it is clear that Bernanke's supporters remain in the majority and do not want to call time on the asset-buying scheme too early. "A few participants noted examples of past instances in which policymakers had prematurely removed accommodation, with adverse effects on economic growth, employment, and price stability," the minutes said.

"They also stressed the importance of communicating the committee's commitment to maintaining a highly accommodative stance of policy as long as warranted by economic conditions."

The Fed plans to evaluate how its programmes are doing at its next meeting March 19 and 20, and Bernanke will answer questions at a press conference following that meeting.

Paul Ashworth, the chief US economist at Capital Economics, described the minutes as "something of an eye-opener". He said the extent of the split within the Fed was not apparent from the statement it released immediately after its meeting on January 30, in which it reiterated its commitment the bond-buying programme.

"In contradiction to what the statement released after the meeting indicated, they suggest that a number of Fed officials might want to 'taper or end its purchases before it judged that a substantial improvement in the outlook for the labour market had occurred'," he wrote in a note to clients.

Dan Greenhaus, the chief global strategist at BTIG, said it was clear that most Fed members were still in favor of Fed policy, and that the Fed was "reconciling the improving economic backdrop with their ongoing asset purchase programme."

"There is clearly support for asset purchases although the implementation is being debated. While there is no talk of ending the program early – something market participants feared following the release of the last minutes – there was talk of tapering the programme off," he said in a note to clients.

The minutes do not identify the dissenting voices, but a number of Fed officials, including Cleveland Fed president Sandra Pianalto and St Louis Fed president James Bullard, have suggested the Fed should scale back its massive buying programme.

The Fed's minutes draw a picture of a long slow recovery. Manufacturing production increased "briskly in November and December after declining in October," said the Fed. "The rate of long-duration unemployment and the share of workers employed part time for economic reasons edged down in December, but both measures were still elevated."

The rate of private-sector hiring "was generally muted but remained consistent with continued moderate increases in employment in the coming months."

The minutes said: "Most participants judged that there had been some reduction in downside risks facing the economy." Fed officials noted the ongoing recovery in the housing market but also noted that mortgage lending remained difficult and many people still owed more than their homes were worth.